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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

HIDDEN, FOURTH AND SMALLER GLACIERS                  165
SMALLEB GLACIERS
Besides the glaciers described in the preceding chapters there are a large number of minor glaciers in the Yakutat Bay region, many of which have as yet received no names. Some of the larger of these were named and briefly described in the reports on our 1905 and 1906 expeditions.1 It does not seem important to repeat these descriptions here, though these glaciers present many interesting features, in detail, one of the most noteworthy being the broad extension of sheets of ablation moraine over their lower surfaces. Many of them resemble the Galiano and Atrevida Glaciers in this respect, though they lack expanded piedmont bulbs, since they no longer extend beyond the mountain front. Some, however, reach far down the mountain valleys, and one or two almost to the valley mouth, ending in low, undulating, moraine-covered surfaces, fringed by barren areas indicative of recent recession.
In 1909, 1910, and 1913 we made no additional observations upon these glaciers except to look at some of them from a distance. From this second view, and from a reconsideration of observations and photographs made in 1905, and in the light of the remarkable changes in some of the other glaciers observed in 1906 and 1909, we have concluded that there is reason for believing that some of these smaller glaciers had been subjected to advance and breaking between 1899 and 1905 as a result of earthquake shaking. Indications of this are best seen in the three glaciers on the west side of upper Russell Fiord, namely McCarty, Hendrickson and Rasmussen Glaciers. In 1905 the lower portions of the last two of these glaciers were completely covered, from side to side, with ablation moraine, having a very rough, hummocky surface. The McCarty Glacier was moderately crevassed but clean in its upper and middle portions (PL LXXXIX, B). Not then knowing the signs of recent advance, which we have since learned to interpret, we did not see, in the conditions of these glaciers, proof of recent advance and breaking. It is to be noted also that we would not have detected evidence of this even in the Galiano Glacier were it not for the fact that we had for comparison Russell's photographs and descriptions of the condition in 1891.
Re-examining the photographs of the small glaciers mentioned, we find the ablation moraine surface to be rough and angular, as if recently broken. It is noted also that there is complete absence of vegetation upon these moraine surfaces. This fact is perhaps the best evidence of recent advance, for the moraine is, in places, thick enough to support a growth of vegetation, and there is abundant alder growth on the hillsides above the glaciers. Its absence, therefore, does not seem possible of explanation either on the theory of failure of vegetation to advance or on the theory of prevention of growth through undermining and slumping. From distant views of these glaciers in 1909, we convinced ourselves that the ablation moraine was less rough than in 1905.
From this reconsideration of the evidence, in the light of subsequent discovery of the nature of phenomena to be expected as a result of a spasmodic advance of glaciers, we are inclined to believe that Galiano Glacier was not the only small glacier in this region to respond to the earthquake impulse prior to 1905. How many glaciers did advance in that interval will probably never be known, but it seems probable that many of the shorter glaciers were subjected to an advance and breaking within a few years after
1 Tarr, R. S. and Martin, Lawrence, Glaciers and Glaciation of Yakutat Bay, Alaska, Bull. Amer. Geog. Soc., Vol. XXXVIII, 1906, pp. 151, 152; Tarr; R. S., The Yakutat Bay Region, Alaska, Professional Paper 64, U. S. Geol. Survey, 1909, pp. 65-68.